Microscope image of the HIV virusq

Although sexual health campaigners are delighted at the news that the Proud trial is being expedited, the arrival of drugs to prevent HIV does not spell the end of Aids. It was discovered several years ago that antiretroviral drugs used to treat people with HIV can also stop people from being infected. There was massive excitement in the Aids community when pre-exposure prophylaxis, or PrEP as it is now known, was proven in trials in 2008 to work. There was a 42% reduction in the numbers of men who have sex with men (MSM) becoming infected with HIV if they were taking the drug Truvada (tenofovir). Those who took the pill every day were 99% protected – a stunning result. In 2012, the US drug licensing body, the Food and Drug Administration, approved the pill for this use.

It is great news that the first stage of the UK trial, which was funded by the Medical Research Council and supported by Public Health England, has been a big success. If the final results are good, public-health experts hope the drug could be made available on the NHS to those at high risk, although negotiations would have to take place with manufacturer Gilead to find a price the health service can afford. The drug can cost the equivalent of £7,500 a year in the US. But as the researchers themselves say, there are still important questions.

One is about people’s willingness to take a pill every day when they are not ill. In the 2008 trial, around half the participants did not take the pills routinely. Medical experience in this and other areas, such as the use of statins for high cholesterol, shows people are reluctant to dose themselves to prevent disease, and HIV drugs can have significant side-effects. One in 10 people on Truvada suffer diarrhoea, dizziness, headaches, rashes, weakness and metabolic problems. It will be good news if a large proportion of the Proud trial participants are happy to take the pills on a regular basis, but what happens in a trial is not always what happens when the trial is over.

Mitchell Warren, executive director of the campaigning US organisation AVAC: Global Advocacy for HIV Prevention, says that people’s preferences vary.

“Bottom line is that PrEP works when you take it correctly and consistently – just like male and female condoms. But also like condoms, not everyone wants to use it, or can or will use it all the time. We know from the most recent data presented in Melbourne [at the International Aids conference in July] that even when offered PrEP freely and with all the accurate information, some people don’t choose it as an option. And some who start it do not use it for long, or consistently. The good news, though, is that many people did use it correctly and consistently and there are remarkably high levels of protection for this group,” he said.

“So PrEP is a classic ‘user-controlled’ option that requires motivation, risk perception, and self-efficacy.”

There are other concerns. Some worry that people taking pills to guard against HIV will take more sexual risks, with more partners. Michael Weinstein, president of the Aids Healthcare Foundation in the US, called Truvada a “party drug”, arguing that it might lead men to have more unprotected sex. Condoms are still crucial to HIV prevention and men in the trials taking the pills have been urged to use them.

PrEP could clearly help people with HIV-positive partners. It would also be an option for anybody in a group known to be at high-risk of infection, such as gay men. But it is not going to do anything to bring down the HIV infection rate in sub-Saharan Africa, where young girls and married women are at risk from older men. There would be cultural barriers to giving the pills to this group. To hand out PrEP implies that they are at risk from a man, possibly a husband, who is having sex with somebody else. And the cost of the drugs would anyway make this prohibitive.

So PrEP, for the foreseeable future, will be confined to highly developed countries such as the US and Britain, where the people most at risk of HIV infection tend to be men who have sex with men – which includes gay, bisexual and transgender women – and the partners of injecting drug users. And even among those groups, it is likely to be an option that some people will choose – and some will not.

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